1. Field of the Invention
The present invention relates to a hand lever device for operating a driven member, such as a throttle valve, of an internal combustion engine via a cable. In particular, the hand lever device is preferably mounted on a working machine, such as a hedge trimmer or brush cutter, in the vicinity of a hand grip so that it is easy and convenient to operate such a throttle valve or the like via a throttle cable or the like.
2. Description of the Prior Art
For example, in a working machine such as a hedge trimmer and brush cutter which comprises an operative portion including a cutting blade or the like driven by an internal combustion engine, a hand lever device is provided for controlling the degree of opening of a throttle valve of the internal combustion engine. Such a hand lever is mounted in the vicinity of a grip of a U-shaped handle, a bar handle or the like of the working machine so as to provide manual control of the output force of the internal combustion engine.
The hand lever device is generally provided with a throttle trigger (throttle lever) operated by operator's fingers with the throttle lever being pivotally operated to thereby control the degree of opening of the throttle valve via a throttle cable. In general, the throttle valve is always biased toward the direction of minimum valve opening that allows the engine to idle. Accordingly, the throttle valve is normally kept at the idle opening position and, when the throttle cable is drawn in a predetermined amount to eliminate play, it begins to open from the opening position for idling (slow running) of the engine toward an opening position for operation (higher speed running) of the engine.
Such known hand lever devices for controlling throttle valve settings include an automatic return to an idle setting type and an immobilizable type. In the former type, when such a throttle lever is released from a pivotally operated position, the lever is automatically returned to its original idle position setting, thereby moving the throttle valve to its idle setting. In the latter type, when fingers are released from a throttle lever, the throttle lever is held immobilized at a desired pivotally operated position (see Japanese Examined Utility Model Publication No.19944/1982, etc.).
In the auto-return type, when fingers are released from the throttle lever, the engine is automatically returned to idling condition. Consequently, when the auto-return type is used in a working machine, where the output force of the engine is transmitted to an operative portion including a cutting blade via a centrifugal clutch, the centrifugal clutch is brought into a condition for disconnection to cut off the transmission of the driving force to the operative portion. Accordingly, the operation of the machinery can immediately be stopped by returning the throttle valve to the opening degree for idle running if an accident occurs, thereby advantageously attaining improved safety. On the other hand, the throttle valve must be held continuously by fingers at a desired pivotally operated position to achieve desired operation of the machinery. This causes problems in that this type is awkward with respect to intermediate opening degrees, the fingers are susceptible to fatigue, and the speed of the engine is likely to be unstable.
In general, it is desired from the viewpoint of operational convenience that a lever which is pivotally operated by fingers, for example, a throttle lever be alternatively shifted between two positions, i.e., a released position and a set position (pressed position) without being suspended at any intermediate position. Accordingly, it is preferred in terms of operability that the lever be set in the same pivotally operated position (set position) regardless of whether an intermediately open condition (partially open condition) or the fully open condition (W.O.T.) of a throttle valve is intended.
On the other hand, the immobilizable type is capable of solving the above problems associated with the auto-return to idle running opening degree type. The immobilizable type advantageously holds the throttle lever at a desired pivotally operated position without the throttle lever being held by the operator's fingers. This enables easy cutting operation because fingers are liberated from holding it. However, since additional operation is required to release the throttle lever from the immobilized position, it is impossible to immediately stop the machinery even if an accident occurs. Accordingly, there is a problem that, in terms of safety, the immobilizable type is inferior to the auto-return to idle running opening degree type.
Further, in either type, when the throttle lever which has once been released to suspend operation is returned to the previous opening degree to resume the operation (as is often the case with a working machine such as a brush cutter), the pivotally operated position of the throttle lever must be readjusted. In view of such cumbersome operation, there is still room for improvement in operability.
To solve the problems in the conventional hand lever devices, the present assignee have previously proposed, for example, a hand lever device comprising a main lever and a sub-lever which are pivotally operated, wherein the sub-lever is adapted to draw a cable connected to a driven member via a cable turnaround member such as a pulley, and the cable turnaround member is moved by the main lever (as disclosed in Japanese Laid Open Patent Application No.303262/1996).
According to such a hand lever device, advantages can be obtained that a throttle valve as a driven member can be adjusted appropriately in its opening degree via a cable and kept at a desired opening degree and yet immediately returned to the minimum opening degree (the opening degree for idle running) to ensure high safety, and that fatigue of fingers can be diminished, and that the throttle valve can be brought to the opening degree at which it had stood before it was returned to the minimum opening degree without necessity of readjustment.
In the proposed hand lever device, however, draw amount of the throttle cable directly corresponds to the amount of the pivotal movement of the main lever. Accordingly, the main lever must be pivotally operated in a relatively large amount in order to draw the throttle cable in a necessary amount. For obtaining a required amount of pivotal movement of the main lever, it is required to provide a relatively large space for pivotal operation of the main lever between a grip of the handle and the main lever. As a result, the hand lever device is not satisfactory in size and weight and also in terms of operability.
To solve the above problem, the present assignee proposed a hand lever device having the following structure as a basic embodiment of the present invention. The proposed hand lever device comprises:
a case to be mounted on a handle,
a main lever pivotally supported by the case for drawing a cable connected to a driven member via a cable turnaround member,
a draw amount magnifying mechanism interposed between the main lever and the cable in the case for magnifying amount of pivotal movement of the main lever to draw the cable in a magnified amount, and
a position adjusting mechanism for moving the cable turnaround member toward the cable drawing direction and holding the cable turnaround member at a desired position.
Incidentally, conventional hand lever devices generally have a case of a binary structure (composed of right and left case members) for supporting/containing movable members such as a main lever, as described, for example, in Japanese Examined Patent Publication No.106098/1995. The right and left case members which constitute the case are put together with a handle held therebetween and they are tightened with bolts or the like to mount the hand lever device on the handle.
In such a conventional hand lever device having a case of a binary structure, however, since movable members such as a main lever are supported/contained between the right and left case members constituting the case, it is difficult to appropriately retain the movable members such as the main lever in (one of) the case members in a time when the right and left case members are separated, i.e., a time when the case is dismounted or separated from the handle, for example, in a time before mounting of the hand lever device on the handle, or in a time of maintenance. Accordingly, mounting of the hand lever device on the handle and maintenance are cumbersome.
Further, since such a conventional hand lever device is mounted on a handle only by putting right and left case members constituting a case together and tightening them with bolts or the like, there is a problem that the case as a whole is likely to rotate or longitudinally move relative to the handle. Such rotation or movement of the case relative to the handle results not only in impairment of operability but also in delicate shift of a front end of the cable. Accordingly, draw amount of the cable is not necessarily constant with respect to given amounts of pivotal movements of a main lever and a sub-lever. Consequently, opening degree of a throttle valve or the like cannot be controlled precisely.